Tool for metal plugging or sealing of casing

ABSTRACT

This disclosure describes a device and method of sealing perforations on a well casing inside a subterranean well. The device comprises a generally cylindrical sleeve having an open top and a closed bottom; a heater located inside the sleeve, the heater comprising a thermite mixture; an ignition mechanism that ignites the thermite mixture upon actuation; and a string connected to the heater ignition and detachably engages the sleeve. The method comprises lowering a body of meltable plugging material into the well casing near the perforations; lowering the plugging device into the well casing immediately on top of the body of meltable plugging material; melting the meltable plugging material by igniting the thermite thereby transferring heat to the body of meltable plugging material; forcing the molten plugging material into the perforations by pushing the plugging tool further downhole; cooling the plugging tool and the plugging material until the plugging material solidifies; disengaging the tubing string from the sleeve and retrieving the tubing string with the heater; and removing the sleeve and bismuth remaining in the well casing, but not in the perforations.

PRIOR RELATED APPLICATIONS

This application is a Continuation claiming benefit under 35 USC § 120to U.S. Ser. No. 15/706,071 (now U.S. Pat. No. 10,760,374, granted Sep.1, 2020), filed Sep. 15, 2017, which is a non-provisional applicationclaiming benefit under 35 USC § 119(e) to U.S. Provisional ApplicationSer. No. 62/402,802 filed Sep. 30, 2016, entitled “TOOL FOR METALPLUGGING OR SEALING OF CASING”, each of which is incorporated herein byreference in its entirety.

FEDERALLY SPONSORED RESEARCH STATEMENT

Not applicable.

FIELD OF THE DISCLOSURE

The disclosure generally relates to a device and method for sealingcasing holes or perforations, particularly to a device and method ofusing metal plugs to seal subterranean casing holes or perforations.

BACKGROUND OF THE DISCLOSURE

Hydrocarbon wells may be abandoned for a variety of reasons, such aswhen dry, when no longer economical to produce, or well integrity hasbeen compromised in some way. It is common practice to plug the wellbefore abandoning it, e.g. to prevent seepage of hydrocarbon productfrom the well. This can also apply to water injectors, i.e. bores whichhave been drilled in order to pump water into a reservoir to increasebottom hole pressure.

It is also possible to abandon only part of a well. One cost effectiveway to enhance production is to permanently abandon the bottom of thewell, but use the existing slot to sidetrack the well to reach newpayzones. The cost can often be cut in half when sidetracking anexisting well instead of drilling a new horizontal well. This process isknown as “slot recovery.”

Plugging can also be temporary, e.g., to allow for workover, a longshut-in, or for converting an exploratory well to a production well. TheNorwegian shelf's competitive position, or NORSOK, standards state thatthe integrity of materials used for temporary abandonment should beensured for the planned abandonment period times two.

In oilfield jargon “plug and abandon” or “P&A” refers to preparing awell to be closed permanently (or at least until prices or technologydevelopments warrant reentry). The earliest oil wells were abandonedwithout any plugging, but the first plugging requirements were enactedby Pennsylvania in the 1890s. However, prior to modern regulations setin the '50s, many wells were abandoned with plugs consisting of brush,wood, paper sacks, linen or any other material that could be pushed intoa well to form a basis for the dumping of one or two sacks of cement to“plug” the well. Current procedures are significantly more disciplined,however.

Commonly, plugging may be achieved by injecting a settable substance ormedium, e.g. cement, into the well. A well will normally have productionperforations, that is to say apertures in a well liner or casing throughwhich hydrocarbon product enters from the rock formation and travels tothe surface. During plug and abandonment operations it is common to seal(“squeeze”) production perforations with cement or another settablemedium, which may then form a permanent barrier to lateral flow acrossthe perforations and in/out of the well.

Other reasons exist to plug or seal a well. For example, one can sealleaks in a well, such as casing leaks. Parts of a well can be shut downfor production or fracking, and the production or fracking moved to adifferent zone. Perforations can also be sealed for water shut off.Thus, there are many reasons for plugging a well or for sealing a casingor a portion thereof.

Usually cement is used for plugging wells or sealing casing, but cementcan be less than satisfactory as it has a tendency to mix with drillingmud or other downhole fluids and this can cause early failure if thefluids cause channeling in the cement. Additionally, cement can bedifficult to pump through perforations in joints, and the cement plugsmay not suffice if the formation is weak. Therefore, in some cases,metal is used in place of cement for plugging and sealing operations.

US20060144591, for example, describes a method and tool for applying afluid seal in a well structure by putting meltable repair material(e.g., eutectic metals or solder) and then ignite exothermic reactantmaterial to melt the meltable material. The molten mass then flows intothe defect and supposedly seal the perforations. However, the discloseddevice only uses thermite sporadically, and positioning of the deviceand plugging material are not customizable or accurate enough to reducethe overall operation cost and time. The device fails to be efficientlyretrieved and reused, especially when the wells need repeat treatment ifnot sealed conforming to legal requirements.

Another heater tool that uses thermite is commercially available fromBiSN Oil Tools, and described in WO2011151271 and WO2014096858. The BiSNWel-lok M2M Bridge Plug™ can run on standard wireline, slick line orcoil tubing. It uses a bismuth-based alloy that is melted in situ usinga chemical reaction (thermite) heater. However, this tool can only heata small volume of alloy at a time. Thus, its applications are limited.

WO2014108431 discloses a method for plugging a hydrocarbon well,including expanding a section of a tubular within the well to contactthe casing lining of the well. The expanded sections are then melted toform a plug for the portions to be plugged. However, it is unclear howthe molten material would flow horizontally into the holes when there isno support from the bottom to push the molten material up and force itto flow laterally.

U.S. Pat. No. 6,474,414, entitled “Plug For Tubulars” is directed to theuse of molten solder for providing a plug in a subterranean well, whichmay be poured or otherwise applied directly upon a platform for themolten solder in the well.

U.S. Pat. No. 9,181,775, entitled “Sealing method and apparatus” isdirected to the use of a mandrel having multiple rings that are spacedapart to allow molten material to solidify between the rings to form aplug. However, this design does not facilitate lateral filling of themolten material in perforations and leaks.

Therefore, there is still the need for a plugging device or tool that isboth efficient for plugging and sealing operations by forcing the moltenmetal plugging material flowing laterally into the perforations andhaving a ignitor that can be reconditioned and reused.

SUMMARY OF THE DISCLOSURE

The present disclosure describes a plugging device or tool foreffectively sealing wells with joint perforations or leaks with metaland retrieving the heater portion of the device after the sealing iscompleted, thus allowing recondition and reuse of the heater andminimizing the amount of material in the well to remove by milling. Thedevice comprises a generally cylindrical sleeve inside of which islocated a heater that comprises thermite that is coupled to andignitable by an ignition mechanism. The sleeve is detachably engaged toa tubing, wireline, coil tubing or other running string that alsoconnects to the ignition mechanism so that it can be retrieved. See FIG.1.

In a plugging or sealing a subterranean well (FIG. 2) a blocking devicemay be deployed first near the bottom section of the section to besealed (unless that section is already at the bottom of the well), so asto provide a physical support as the starting point of the operation. Abody of meltable plugging material is then placed into the well near theperforations or leaks to be sealed, and sits on top of the blockingdevice. The meltable plugging material can be dropped from the surfaceand be in the form of pellets, balls, or other shapes. The top of themeltable plugging material can be determined by volumetric measurementor by running a measurement instrument on wireline.

Alternatively, the meltable material can be molded into a solidcylindrical form that surrounds the sleeve, which is attached to theheater/ignitor assembly. When the heater is ignited, the molded alloyoversleeve melts, falling down onto the base plug and provided the metalplug or seal on re-cooling.

The plugging tool described herein is then introduced into the well tosit immediately above or on the meltable plugging material. Whenignited, the heater undergoes a redox reaction and transmits heatthrough the sleeve to the immediately adjacent meltable pluggingmaterial. The meltable plugging material begins to melt, and theplugging device descends further down the well through the moltenplugging material, thus forcing the plugging material against the wellcasing by minimizing its axial movement and promoting its lateralmovement into the perforations. Thus, the tool can melt several feetworth of plugging material if needed, and has much larger capacity thatprior art tools.

In yet another embodiment, the heater is sent down first, and thepellets dropped around the heater.

In the embodiment of the tool with an molded oversleeve of alloy, it isplaced on the bottom on the blocking device. The thermite is ignited andthe heat melts the material from surrounding the sleeve, thus fillingthe area to be plugged over the base plug from the bottom up.

Once the thermite is depleted the plugging device and the moltenplugging material is allowed to cool down. The molten plugging materialsolidifies and adheres to the well casing as well as to the sleeve andany reservoir wall it contacts. The sleeve is then disengaged from theheater, which is pulled with the tubing or other string, which is thenretrieved to the wellhead along with the ignition mechanism. The sleeveand/or residual plugging material can then be removed by a mill ordrill, if desired, and optionally the well is evaluated to determinewhether seal is sufficient. If desired, the drilled/milled section canbe fully plugged to provide a permanent or temporary plug.

In more detail, the invention includes any one or more of the followingembodiment(s), in any combination(s) thereof:

A device sealing perforations or leaks in a well, comprising: a) agenerally cylindrical sleeve having an open top and a closed bottom;b) a heater located inside the sleeve, the heater comprising a thermitemixture; c) an ignition mechanism that ignites said thermite mixtureupon actuation, said ignition mechanism inside said sleeve andcontacting said thermite; and d) a line detachably connected to saidsleeve and connected to said ignition mechanism, such that said sleevecan be detached and left behind when said ignition mechanism isretrieved from a subterranean well. A system for sealing perforations orleaks in a well casing or tubular in a subterranean well, comprising:a) a generally cylindrical sleeve having an open top and a closedbottom; b) a heater located inside the sleeve, the heater comprising athermite mixture; c) an ignition mechanism that ignites the thermitemixture upon actuation, d) a line connected to said ignition mechanismand detachably engaging said sleeve; and e) a body of meltable pluggingmaterial that is either 1) molded over an outside of said sleeve or 2)placed as pellets a zone to be sealed; and f) a blocking device at orbelow a bottom end of said zone to be sealed, which can be a wellbottom, plug, or other mechanical blocking device, or a non-mechanicalblocking device such as a sand plug, sandbag, resin, sand, and the like.A method for sealing a well casing in a subterranean well, comprising:a) lowering a blocking device into a well to block a bottom of a zone ofa well to be sealed, unless said zone is already blocked with a blockingdevice; b) lowering a body of meltable plugging material into said wellto rest on said blocking device; c) lowering a plugging tool into thewell casing immediately on top of the body of meltable pluggingmaterial, the plugging tool comprising a generally cylindrical sleevehaving an open top and a closed bottom, a heater located inside thesleeve, the heater comprising a thermite mixture, an ignition mechanismthat ignites the thermite mixture upon actuation, and a line connectedto said ignition mechanism and detachably connected to said sleeve;d) melting the meltable plugging material by igniting the thermitethereby transferring heat to the body of meltable plugging material;e) cooling the plugging tool and the plugging material until theplugging material solidifies; f) disengaging said line from said sleeveand retrieving said line with the ignition mechanism; and g) drillingout or milling out said sleeve. A method for sealing a well casing in asubterranean well, comprising: a) lowering a blocking device into a wellto block a bottom of a zone of a well to be sealed; b) lowering aplugging tool into the well casing immediately on top of the blockingdevice, the plugging tool comprising a generally cylindrical sleevehaving an open top and a closed bottom, a heater located inside thesleeve, the heater comprising a thermite mixture, an ignition mechanismthat ignites the thermite mixture upon actuation, and a line connectedto said ignition mechanism and detachably connected to said sleeve,wherein a meltable plugging material is molded on the outside of thesleeve; c) melting the meltable plugging material by igniting thethermite thereby transferring heat to the body of meltable pluggingmaterial; d) allowing the plugging tool to descend further downhole tofurther melt the meltable plugging material; e) cooling the pluggingtool and the plugging material until the plugging material solidifies;f) disengaging said line from said sleeve and retrieving said line withthe ignition mechanism and exhausted thermite residue; and g) drillingout or milling out said sleeve. Any device or system or method hereindescribed, wherein said sleeve has an outer diameter (e.g., ¼ inch,½inch, 1 inch, 1.5 inch) smaller than the inner diameter of the wellcasing. Any device or system or method herein described, wherein thethermite is nano-thermite. Any device or system or method hereindescribed, wherein said ignition/heater mechanism is a drop barignition, a pressure ignition, or a wireline ignition. Any device orsystem or method herein described, further comprising a meltableplugging material molded around an outside surface of said sleeve. Anydevice or system or method herein described, wherein said line is tubingstring, wireline, coiled tubing, and the like. Any device or systemherein described, further comprising a leak detector selected from aninfrared detector, an acoustic energy detector, and a camera. Any deviceor system or method herein described, wherein the meltable pluggingmaterial is an expandable bismuth alloy. Any method herein described,further comprising, after drilling/ milling step: evaluating the sealedsection of the well casing to determine whether sealing is complete. Anymethod herein described, further comprising, after lowering the pluggingtool step: determining the optimal location to place the plugging toolby detecting the actual leakage on the well casing. Any method hereindescribed, further comprising the step of plugging the sleeve with ameltable alloy, resin, cement or other material. Any method hereindescribed, further comprising drilling out or milling out the sleeve,and plugging the remaining volume with a meltable alloy, resin, cementor other material.

As used herein, a “P&A” refers to plug and abandon. Regulations requirethat the plugs be of sufficient quality to be“permanent,” never allowingformation fluids to leak. However, it is recognized that even apermanently plugged and abandoned well may be reopened at a later timefor various reasons. Therefore, “permanent” does not imply that the wellwill not be reopened, but instead refers to the quality of the plug—itneeding the potential to last along time.

As used herein, “sealing” a casing or production tubular stops thecasing or tubular from leaking, e.g., transfer of fluid from outside thecasing to the inside and vice versa (lateral flow) is prevented.However, fluids may still flow through the interior of the casing orproduction tubing (longitudinal flow). In contrast, “plugging” refers topermanent or temporary plugging and stops both lateral fluid flow acrossthe casing/tubulars as well as longitudinal fluid flow inside thecasing/tubulars, and would be suitable for P&A operations. See e.g.,FIG. 3 showing rock-to-rock plugging in both lateral and verticaldirections.

As used herein, a “blocking device” is any device used to prevent cementor alloy from falling downhole, e.g., it provides a stable base on whichto set e.g., a cast-in-place plug. This can be a mechanical device, suchas basket, inflatable basket, plug, packer, or metal plug placed bymelting Bismuth alloy or other metal and the like.

The blocking device could also be a cement plug, barite plug, sand plug,resin plug, combinations thereof, a bolus of extra heavy mud, or anyother non-mechanical blocking device. Since this only acts as a base fora plug, it is not required to act as a permanent plug by itself, and therequirements may be less stringent.

“Tubular” or “tubing” can be used generically to refer any type ofoilfield pipe, such as drill pipe, drill collars, pup joints, casing,production tubing and pipeline. However, generally we have referred tothe inner tubing, such as injection tubing or production tubing astubulars herein. The outer one or more tubing sets, we have referred toas “casing” herein.

As used herein, a “joint” is a length of pipe, usually referring todrill pipe, casing or tubing. While there are different standardlengths, the most common drill pipe joint length is around 30 ft [9 m].For casing, the most common length of a joint is 40 ft [12 m].

As used herein, a “tubular string” or “tubing string” refers to a numberof joints, connected end to end (one at a time) so as to reach down intoa well, e.g., a tubing string lowers a sucker rod pump to the fluidlevel.

As used herein the “wellhead” refers to the surface termination of awellbore that incorporates facilities for installing casing hangersduring the well construction phase. The wellhead also incorporates ameans of hanging the production tubing and installing the Christmas treeand surface flow-control facilities in preparation for the productionphase of the well.

As used herein, “thermite” means a pyrotechnic composition of metalpowder fuel and metal oxide. When ignited by heat, thermite undergoes anexothermic reduction-oxidation (redox) reaction. Examples of the metalin thermite compositions include but not limited to aluminum, magnesium,titanium, zinc, silicon, and boron. Examples of the oxidizers in termitecompositions include but not limited to bismuth (III) oxide, boron (III)oxide, silicon (IV) oxide, chromium (III) oxide, manganese (IV) oxide,iron (III) oxide, iron (II, III) oxide, copper (II) oxide, and lead (II,IV) oxide.

The use of the word “a” or “an” when used in conjunction with the term“comprising” in the claims or the specification means one or more thanone, unless the context dictates otherwise.

The term “about” means the stated value plus or minus the margin oferror of measurement or plus or minus 10% if no method of measurement isindicated.

The use of the term “or” in the claims is used to mean “and/or” unlessexplicitly indicated to refer to alternatives only or if thealternatives are mutually exclusive.

The terms “comprise”, “have”, “include” and “contain” (and theirvariants) are open-ended linking verbs and allow the addition of otherelements when used in a claim.

The phrase “consisting of” is closed, and excludes all additionalelements.

The phrase “consisting essentially of” excludes additional materialelements, but allows the inclusions of non-material elements that do notsubstantially change the nature of the invention.

The following abbreviations are used herein:

ABBREVIATION TERM P&A Plugging and abandoning

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows the tool of this disclosure.

FIG. 1B shows the tool having a meltable material molded over it,forming a cylindrical oversleeve, surrounding the sleeve.

FIG. 2A-I shows the method using the tool of this disclosure.

FIG. 3 shows basic plugging.

DETAILED DESCRIPTION

FIG. 1A shows the novel tool of this disclosure. The tool is designedfor efficient sealing of perforations or leaks in the well casing orproduction tubulars in subterranean wells. The device 100 comprises acylindrical sleeve 101 with a closed bottom or base inside whichthermite 103 is located. The thermite 103 is coupled to an ignitionmechanism 107, also inside the sleeve 101 so as to ignite the thermite103 and start the exothermic reaction.

When the alloy melts, it will have a consistency like water, and fillall gaps between the sleeve and reservoir wall, thus filling anyperforations. If an expandable alloy is used, it will continue toexpands as it cools, being pushed radially into good connection or bondwith the reservoir wall. Any small gaps between the base plug and thewall are easily filled by the cooling alloy front, thus filling suchgaps, and very little is lost to leakage.

The sleeve and heater can be 1 to 10 m or more in length and holds 25 to500 pounds of thermite mixes of various thermite concentrations, thushaving the heat capacity to melt up to 50-2000 pounds of alloy. Whenfully deployed, the abandonment plug ranges from 1-10 meters in length,and this great length has sufficient integrity to provide a permanentabandonment plug or seal holes and/or perforations allowing otheroperations after cleaning the wellbore out through the section. Forlarger bore plugs, or for longer lengths of perforations, the plug canbe set in stages, adding one or more layers on top of the initial plug.

The sleeve 101 and the thermite heater 103 are detachably connected to arunning tool that is attached to a work string 105 and can be releasedby triggering a release mechanism 109. The running tool can also beattached to a wireline, a coil tubing, or a running string tubing ordrill pipe or other work string. The release mechanism 109 can be ashear release. Thus, the sleeve can be left downhole, and the workstring105 can retrieve the ignition element 107. The string 105 connects tothe retrieving equipment, wireline, coil tubing or drilling unit so thatthe igniter 107 and heater 103 can be retrieved. Thus, when detached,the ignitor, and any remaining heater or thermite product will be pulledfrom the hole, leaving a sealed casing behind, lined with the sleeve,which is bonded to the alloy.

The sleeve is made of a strong material that has longitudinal strengthand good heat/chemical resistance to be used in the subterraneanenvironment. Further, the sleeve preferably has thin walls that areeasily drillable for lighter weight, and for easily removable by a millor drill upon completion of plugging. In one embodiment, the sleeve ismade of thin metal of about ⅛″ inches of steel. Thus, if desired, it caneasily be removed, leaving a clean casing for further downhole work, orit can then be further plugged with additional alloy or other materials.Alternatively, the sleeve can be further plugged, with melted alloy orother material.

The heat generated by the thermite is controlled, for example, by itscomposition that is designed for a particular material and length oftime, such that the sleeve and other parts of the system would not bemelted. Also in most cases thermodynamics inside the well will removeexcess heat from the sleeve, preventing it from being melted.

The exterior diameter of the plugging tool 100 is such that it canloosely slide inside the well casing and allow for a small gap betweenthe inner surface of the casing and the outer surface of the tool. Thegap is to reduce undesirable wear and tear when lowering the tool intothe well, to accommodate minor deviations in the tubulars, and also toallow molten plugging material to flow upward when the sleeve physicallydisplaces the molten plugging material inside the well. If the gap islarger, then more plugging material is required. In a preferredembodiment, the gap is about ⅛″ to ½″, for example, in a 10¾″ pipe, theplugging tool can have a diameter of 9¾″ to 10½″.

In another variation the sleeve has bismuth alloy 120 or other materialmolded or attached to it in the form of an oversleeve, as shown in FIG.1B. In this case the sleeve and heater are smaller in diameter. Themolded alloy has a thickness to allow for a small gap between the innersurface of the casing and outer surface of the tool.

The ignition mechanism is not limited, as long as the thermite can beproperly ignited. Typically, in the metal/metal oxide thermite, theignition temperature is extremely high. Ignition of a thermite reactionnormally requires a sparkler or easily obtainable magnesium ribbon, butmay require persistent efforts, as ignition can be unreliable andunpredictable.

The two most common ways to ignite thermite are: magnesium ribbon (Mg)and potassium permanganate (KMnO₄)+glycerin. Magnesium metal burns in anoxygen environment (air) in a very bright, exothermic reaction.Magnesium ribbon can burn at several thousand degrees easily ignitingthermite. The magnesium ribbon is useful as it acts like a fuse, calmlyburning, allowing a short delay between when the ribbon is lit and whenthe thermite begins to react. Potassium permanganate is an extremelypowerful oxidizer which spontaneously ignites after coming in contactwith glycerin. After adding a few drops of glycerin to potassiumpermanganate powder and a short delay, a violent exothermic oxidationreaction occurs which will ignite a thermite mixture.

The ignition mechanism can be a drop bar ignition, a pressure ignition,a wireline ignition, or other suitable mechanism. A drop bar ignites thethermite through its physical impact on a firing head, which burns to ahigh temperature thus igniting the thermite.

A thermite can also be ignited under high temperature and pressure. Bycreating a sealed chamber adjacent to the thermite, a sudden increase ofpressure by compressing the chamber accompanied by setting off themagnesium ribbon, the thermite can be ignited.

A wireline ignition uses an electrically conductive wireline connectingto a resistive material surrounded by a thermite material, such thatwhen electricity flows through the wireline into the resistive material,which heats up to the ignition point of the thermite material andignites it.

The running string engages the heater, by connectors (not shown)provided between the heater and the tubing string. The heater is thenengaged to the sleeve by friable latches, shear pins, or other removableconnectors. The shear force of an attempted withdrawal will break thefriable latches, shear pins or other connectors because the sleeve isbonded to the now solidified plugging material, thus resistingwithdrawal. This allows the heater to detach from the sleeve, allowingthe beater and thermite remnant to be retrieved, leaving the sleevebehind.

FIGS. 2A-I show the method of present disclosure using the tool as shownin FIG. 1.

In FIG. 2A, the subterranean well 230 has a plurality ofperforations/holes 232 that need to be plugged before abandoning thewell or that need to be sealed for other reasons. The perforations/holes232 may or may not be interconnected, but herein shown are perforationsin an outer casing that is otherwise cemented, thus the perforationsreach to or into the reservoir rock and the cement remains betweenperforations. The bottom of the well zone 230 has been blocked, forexample by a blocking device or the bottom of the well, so that themeltable plugging material and the tool can be accurately positioned.

The plugging apparatus and method of this disclosure can be used onexterior perforations as well as leaking casing, so long as theapparatus and the meltable material can fit inside the wells needed tobe plugged. Thus, heater sleeve size is adjusted for well diameter.

In FIG. 2B, the meltable plugging material 220 is lowered to the portionof well that needs to be sealed or plugged. Here the plugging material220 is positioned with the help of the blocking device. This materialcan be dropped from surface in the form of pellets, balls, or othershapes. The top of this material can be determined by running tools onwireline.

The plugging material 220 in this case is preferably a low melt alloy inthe form of pellets. Low melt alloys or fusible alloys are alloys with alow melt temperature and that can expand up to 3.32% when solidifyingfrom a liquid to a solid depending on the product. This expansion allowsthese alloys to precisely conform to any intricate details when molded.In a cast-in-place plug or seal, the expansion means that the plug willexpand to firmly contact the reservoir walls, as well as any cement andmetal casing or tubing, and provide a tight seal. Further, since thepreferred expandable alloys continue to expand as they cool, alloy willbe forced into tiny cracks, channels, fractures and the like, providingan excellent barrier.

Bismuth alloys are a preferred cast-in-place material because bismuthexpands 1-3.32% on solidification. Bismuth also has unusually lowtoxicity for a heavy metal. Furthermore, we have tested these alloys andknow that the liquid alloy does not mix with other fluids, like cementdoes. Thus, the channeling common in cement plugs is avoided.

Exemplary alloys are described in U.S. Pat. No. 7,290,609. As a generalrule, bismuth alloys of approximately 50% bismuth exhibit little changeof volume (1%) during solidification. Alloys containing more than thistend to expand during solidification and those containing less tend toshrink during solidification. Additional alloys are described inUS20150368542, which describes a bismuth alloy comprises bismuth andgermanium and/or copper. Additional eutectic alloys to plug wells orrepair existing plugs in wells are described in U.S. Pat. No. 7,152,657;US20060144591; U.S. Pat. Nos. 6,828,531; 6,664,522; 6,474,414; andUS20050109511. Other bismuth alloys can also be used, while bismuth tinor bismuth lead or bismuth aluminum are most common.

In FIG. 2C, the plugging tool 200 with thermite 203 inside the sleeve201 is lowered into the portions to be plugged inside the well. Theplugging tool 200 is positioned on top of the meltable pluggingmaterial. As discussed above, the amount of meltable plugging materialcan be measured against the well diameter to obtain the exact locationof its top. Or alternatively, when previously dropping the meltableplugging material 220, the associated wireline has a known length thatcan be used to determine where the plugging tool 200 should bepositioned.

If preferred, melting can be started from the bottom, by first deployingthen tool, and then dropping pellets into the well. This may bebeneficial for sealing any annular space at the bottom first.

In the next step, the thermite 203 is ignited by the ignition mechanismin the plugging tool 200. Here the thermite can be a conventionalthermite, or Applicant's co-pending nano-thermite. See co-pendingUS20180094504. Nano-thermite is an especially useful material because itrequires less heat to initiate the thermite reduction-oxidationreaction, and the volume of the material can be tuned to each well beingplugged. Additionally, the small size of particles increases the amountof surface area for the reaction, which in turn increases the reactionrate and produced heat, thereby allowing the plug to be set quicker thanone using conventional thermite.

Once ignited, the exothermic reaction will heat the sleeve andsurrounding meltable bismuth alloy previously deposited inside the well,beginning to melt it. The well casing itself is a large heat sink todirect and dissipate the excess heat on the sleeve away, thus preventingthe sleeve from being melted. The composition of the thermite can alsobe tailored for different type and amount of bismuth alloys.

In FIG. 2D, molten bismuth alloy allows the plugging tool 200 to descendfurther into the well, at the same time the molten bismuth is pushed upalong the well and into the perforations. This is important andbeneficial, because the physical space occupied by the plugging tool 200forces the molten bismuth into the perforations instead of into spacethat is otherwise inaccessible by the prior art tools. The more thebismuth is melted, the further down the plugging tool 200 travels todisplace molten bismuth and push it into the perforations. Further, alarger volume of meltable material can be melted using the tool of theinvention than with prior art tools.

In FIG. 2E, the plugging tool 200 eventually reaches to the bottom ofthe well (or the blocking device), and at this time all bismuth has beenmelted, and all perforations are filled with molten bismuth as well. Ifthe casing is not cemented, a small amount will run down the exterior ofthe casing, but the gap is typically not very large, and the alloy willcool as it leaves the heated zone, coming to a stop. Heated alloy willdrip over the cooled zone, itself cooling and building up the solidportion, until it eventually plugs the annulus completely. Where thecasing is cemented, the alloy fills the perforations, and any cracks orcrumbled cement, as well as fractures in the reservoir wall. As thealloy continues to cool, it will expand and be forced into tight contactwith its surroundings, forming a very good seal.

In FIG. 2F, the thermite inside the plugging tool 200 is exhausted, andboth the tool and the bismuth alloy are allowed to cool down andsolidify. Once the bismuth is solidified, the tool 200 detaches from thesleeve 201 by disengaging the release mechanism (see FIG. 1,109),leaving the sleeve in place while the string 205 pulls the ignitorportion of the tool 200 away, along with the solid exhausted thermite.As noted above, the sleeve release mechanism can be pressure based, thussnapping as the heater is pulled up, or an active release mechanism(e.g. a magnetic or electric latch), can be triggered by wireline.

Leaving the sleeve portion of the tool in place and retrieving just theheater is beneficial. Not only are the heater components retrieved forreuse, allowing the use of more efficient electrical ignitors, but thesleeve reduces the amount of molten alloy needed to seal the casing (ortubular). It also allows much more molten material to be generated thanprior art tools, which were completely retrieved, instead of beingallowed to penetrate and melt a larger volume of material in asequential fashion.

In FIG. 2G, the tool 200 is completely removed from the well, while thesleeve 201 is still held in place by the re-solidified bismuth alloy orother material. The fact that the sleeve 201 is left in place actuallyfacilitates the removal of tool 200. The solid thermite product (afterredox reaction) will be retrieved along with the heater.

In FIG. 2H, a mill 211 (or a drill that has appropriate diameter) isintroduced inside the well in order to mill and destroy the sleeve 201and optionally residual bismuth in the gap between the casing interiorand sleeve exterior, leaving only the perforations with filled bismuth,which completely plugs the holes, as shown also in FIG. 2I. Thisprovides a sealed casing, with completely smooth interior surface,allowing further downhole work.

If instead of a seal, a permanent plug is desired, then the centralmilled or drilled region can be further plugged by deploying a blockingdevice to the base of the area to be plugged, and then the space filledwith cement, resin, sandbag, geopolymer, cast-in place bismuth alloyplug, and the like. It may not even be necessary to mill out the sleeve,but leave it in place, depending on the material durability andregulations. Alternatively, a bridge plug can be used, that is e.g.,capped with cement. This complete plugging can be done by methods knownin the art, or by new methods described for example in US20190128092 andU.S. Ser. No. 10/738,567. Nevertheless, using the methodology employedherein, we have ensured that the original perforations and/or leaks arepermanently sealed all the way to the formation wall.

In another embodiment, the bismuth alloy or other metal can be moldedonto the outside of the sleeve, forming a second sleeve or “oversleeve”.The assembly is run and the bottom tagged. The heater is then ignitedand the heat melts the alloy from the heater and into the perforations(or holes). The metal re-solidifies, thereby holding the sleeve in placeand facilitates removal of the heater.

Test 1

Applicant tested the plugging tool of this disclosure comparing toexisting sealing method. It is discovered that the time for pluggingoperations is shortened by at least 30%, primarily because theintegrated tool removal mechanism and customizable nano-thermite.Further, a larger zone can be sealed that was previously possible withthe smaller prior art tools, and the amount of sealing material per unitof well length is reduced.

The following references are incorporated by reference in theirentirety.

US20050109511, Oil and gas well alloy squeezing method and apparatus

US20060144591 Method and apparatus for repair of wells utilizingmeltable repair materials and exothermic reactants as heating agents

US20150368542 Heat sources and alloys for us in down-hole applications

US20160145962 WO2011151271 WO2014096858 Apparatus for Use in WellAbandonment

US20180094504, Nano-thermite Well Plug

US20190128092, Through Tubing P&A with Bismuth Alloys

U.S. Pat. No. 6,474,414 Plug For Tubulars

U.S. Pat. No. 6,474,414 Plug For Tubulars

U.S. Pat. No. 6,664,522 Method and apparatus for sealing multiplecasings for oil and gas wells

U.S. Pat. No. 6,664,522 Method and apparatus for sealing multiplecasings for oil and gas wells

U.S. Pat. No. 6,828,531 Oil and gas well alloy squeezing method andapparatus

U.S. Pat. No. 7,152,657 In-situ casting of well equipment

U.S. Pat. No. 7,290,609 Subterranean well secondary plugging tool forrepair of a first plug

U.S. Pat. No. 9,181,775 Sealing method and apparatus

U.S. Ser. No. 10/738,567, Through tubing P and A with two-material plugs

WO2014108431 A method for plugging a hydrocarbon well

The invention claimed is:
 1. A device for sealing perforations or leaks in a well, comprising: a) a generally cylindrical sleeve having sides and an open top and a closed bottom; b) a heater located inside said sleeve, said heater comprising a thermite; c) an ignition mechanism inside said sleeve and contacting said thermite that upon actuation ignites said thermite; and d) a line detachably connected to said sleeve, said line connected to said ignition mechanism, such that said sleeve can be detached and left behind to form a sealed casing with said sleeve exterior bonded to a plugging material when said ignition mechanism is retrieved from a subterranean well.
 2. The device of claim 1, wherein said thermite is a nano-thermite.
 3. The device of claim 1, wherein said ignition mechanism is a drop bar ignition, a pressure ignition, or a wireline ignition.
 4. The device of claim 1, wherein said line comprises a tubing string or wireline or coiled tubing.
 5. The device of claim 1, wherein said device further comprises a leak detector selected from an infrared detector, an acoustic energy detector, and a camera.
 6. The device of claim 1, wherein said device further comprises a cylindrical oversleeve made of a meltable plugging material molded around an outside surface of said sleeve.
 7. The device of claim 6, wherein said meltable plugging material is a eutectic alloy.
 8. The device of claim 6, wherein said meltable plugging material is a bismuth alloy.
 9. A method for sealing a well casing in a subterranean well, comprising: a) lowering a blocking device into a well to block a bottom of a zone of casing having one or more perforation(s), unless said zone is already blocked with a blocking device; b) lowering the device of claim 1 into said well to said zone; c) lowering a body or pellets of a meltable plugging material to said zone; d) actuating said ignition mechanism and igniting said thermite to produce molten plugging material; e) cooling said molten plugging material until said molten plugging material solidifies in a space between a wall of said well and an exterior of said sleeve and filling said perforation(s); and f) disengaging said line from said sleeve and retrieving said line and said ignition mechanism without retrieving said sleeve, wherein an amount of said meltable plugging material is less than would be required by a method that removes said sleeve.
 10. The method of claim 9, further including the step of squeezing said molten plugging material before said cooling step e) to force said molten plugging material into said perforation(s).
 11. The method of claim 9, wherein said meltable plugging material is a eutectic alloy.
 12. The method of claim 9, further comprising, after step f) evaluating said zone to determine whether said perforation(s) are completely sealed.
 13. The method of claim 9, further comprising first determining an optimal location to place said device by detecting a location of said perforation(s).
 14. The method of claim 9, further comprising step g) drilling out or milling out said sleeve.
 15. A method for sealing a well casing in a subterranean well, comprising: a) lowering a blocking device into a well casing to block a bottom of a zone of a well to be sealed, unless said zone is already blocked with a blocking device; b) lowering the device of claim 6 to said zone; c) actuating said ignition mechanism and igniting said thermite to melt said oversleeve resulting in molten plugging material; d) cooling said molten plugging material until said molten plugging material solidifies in a space between a wall of said well and an exterior of said sleeve; and e) disengaging said line from said sleeve and retrieving said line with the ignition mechanism without retrieving said sleeve, wherein an amount of said meltable plugging material is less than would be required by a method that removes said sleeve.
 16. The method of claim 15, further including the step of squeezing said molten plugging material before said cooling step d) to force said molten plugging material into one or more perforation(s) in said zone.
 17. The method of claim 15, wherein said meltable plugging material is a eutectic alloy. 